The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
An electric-powered induction motor transforms electric power to mechanical torque by inducing rotating magnetic fields between a static element, i.e., a stator, and a rotatable element, i.e., a rotor. The rotating magnetic fields generate torque on a shaft coupled to the rotor through conductor bars. Known stators induce current flows through conductor bars on the rotor that are preferably parallel to an axis of rotation of the rotor.
A known rotor for an induction motor includes a stack of steel sheets (i.e. laminated steel stack) assembled onto a rotatable shaft, and a plurality of conductor bars fabricated from conductive material, e.g., copper or aluminum. The conductor bars are contained in conductor bar grooves axially defined at the periphery of the laminated steel stack and are preferably connected at both axial ends of the rotors using shorting end rings.
Known rotor fabrication methods include placing the laminated steel stack into a casting mold and introducing molten material into open spaces formed in the rotor and open spaces between the die cast mold and the laminated steel stack to form the shorting end rings and conductor bars. It is known that oxide inclusions and voids may be formed in the conductor bars and shorting end rings during mold filling of molten material and solidification. The molten material may cool and partially solidify during turbulent flow of the molten material into the plurality of conductor bar grooves due in part to exposure to surface areas of the conductor bar grooves. The partially solidified molten material may impede molten material flow and cause voids, oxide inclusions, and other discontinuities in the conductor bars and the shorting end rings.
Power density output from an electric induction motor correlates to quality of the conductor bars and mass bulk density of the individual conductor bars. It is known that voids formed in the conductor bars and the shorting end rings during fabrication reduce power density output of the electric induction motor. The presence of oxide occlusions and cracks due to hot tearing reduces the electrical conductivity of the conductor bars and shorting end rings, thereby reducing the power density of the motor.
The use of copper material for conductor bars and/or shorting end rings may increase power density and heat transfer characteristics of an induction motor as compared to an induction motor using aluminum conductor bars and aluminum shorting end rings. Known use of copper material for conductor bars and shorting end rings increases manufacturing process times and complexity as compared to aluminum conductor bars. Known manufacturing processes for manufacturing conductor bars and shorting end rings include casting the conductor bars and shorting end rings in place around the laminate stack. Another approach is to pre-manufacture the conductor bars and shorting end rings for assembling onto the laminate stack to be welded or brazed in place.